Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to fuel injectors. As one example, a fuel delivery system can utilize an electrically driven lower pressure pump (i.e., a fuel lift pump) and a mechanically driven higher pressure pump arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage.
In such a configuration, the lift pump is operated to prevent unintended vaporization in the higher pressure pump. Low inlet fuel pressure, high fuel volatility, high higher pressure pump speed, and high higher pressure pump temperature in such a configuration may result in reduced pump volumetric efficiency and/or reduced lubrication of the higher pressure pump. As such, a measure of fuel volatility (e.g., fuel vapor pressure) may be used to determine a minimum required lift pump energy. However, this results in using more lift pump energy than needed to cover uncertainty in preventing unintended fuel vaporization, resulting in reduced fuel efficiency. Further, if an unanticipated pressure loss occurs (e.g., due to a clogged filter), a feedforward-only system cannot compensate for this, and fuel vaporization may occur, resulting in fuel starvation or pump lubrication issues.
The inventors herein have recognized the above issues, and have devised an approach to at least partially address them. Thus, a method for a gasoline direct injection engine system is disclosed. In one example, the method includes operating a fuel lift pump at a pressure within a threshold range above a fuel vapor pressure. The fuel vapor pressure may be determined based on a fuel capacitance sensor, for example.
By operating the fuel lift pump at a pressure greater than the fuel vapor pressure, the fuel may be prevented from vaporizing at the higher pressure pump. As such, fuel starvation and/or pump lubrication issues may be reduced. Further, because the vapor pressure is determined based on fuel capacitance from a sensor such as a fuel composition sensor, the sensor may provide feedback regarding the fuel vapor pressure such that the lift pump is not operated at a pressure higher than required and fuel system efficiency may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.